Conventional techniques for locating wireless emitters (e.g., access points and laptops) are typically based on measuring the amplitude of the emitter with a portable receiver, and moving around to find the direction in which the amplitude increases. The general assumption is that the stronger the signal amplitude, the closer the emitter is believed to be. Several commercial devices were developed for this purpose (e.g., Yellowjacket® 802.11b Wi-Fi Analysis System).
There are a number of problems associated with such amplitude-based techniques for locating wireless emitters. For instance, the techniques tend to be highly inaccurate due to the incidence of RF multipath created by the RF waveforms emanating from the wireless emitters. These waveforms bounce off conductive objects or surfaces in the environment, which causes multiple false readings on increased amplitude (false directions) that then disappear as the user leaves the multipath. Thus, conventional amplitude-based locationing techniques will create many false high amplitude paths to the target that will be incorrect, and will not work in a high multipath environment, such as a neighborhood (e.g., street scene) or building (e.g., home, office building, or cafe). Moreover, emitter devices that are not currently powered-on are not detectable. In addition, some electronic devices, such as passive receivers that are not designed to intentionally emit energy, are not detectable using conventional locationing techniques.
There is a need, therefore, for techniques that allow for the detection, identification, and geolocation of wireless emitters. In a more general sense, there is a need for locationing of communication receiver devices.